2025-01-10
Disentangling the effects of size, exposure and water availability on drought sensitivity of tree growth
\(sensitivity_{tree} = \frac{drought.year.increment - mean.annual.increment_{tree}}{mean.annual.increment_{tree}}\)
| Variable | Description |
|---|---|
| sensitivity | Late wet/early dry dendrometer band measurements |
| exposure | Crown Illumination index at previous dendroband census |
| size | DBH at previous dendroband census |
| water | Topographic wetness index |
How well do species traits predict average sensitivity of species?
\(sensitivity_{tree}~ 1+ (1|Species)\)
We ran 3 different models
varying intercepts by species
\(sensitivity_{tree} = \beta_{DBH}DBH_{0} + \beta_{TWI}TWI + \beta_{CII}CII_{0} + (1|Species)\)
varying intercepts + predictors scaled within species
\(sensitivity_{tree} = \beta_{DBH}DBH_sp_{0} + \beta_{TWI}TWI_sp + \beta_{CII}CII_sp_{0} + (1|Species)\)
varying slopes + predictors scaled within species
\(sensitivity_{tree} = \beta_{DBH}DBH_sp_{0} + \beta_{TWI}TWI_sp + \beta_{CII}CII_sp_{0} + (1+DBH+CII+TWI|Species)\)
Variation in sensitivity among individuals was explained more by crown exposure than size per se
To corroborate these results we modelled growth occurrence as a binary response.
And found similar, stronger influence of exposure on growth occurrence
This implies mediation effects of size on exposure